基于黄金分割法的双季稻合理密植研究

为了验证水稻合理密植的黄金分割法在长江中下游双季稻区和华南双季稻区的适用性,在湖南长沙和广东怀集以生产上大面积种植且具有代表性的双季稻品种为材料,运用黄金分割法分割秆高(50、65、80、95、110 cm)得到5种预设黄金密度(67.9、40.1、26.5、18.8、14.0穴·m-2),研究不同密度下株高和秆高的变化,实际黄金密度下齐穗期部分冠层特性、干物质积累、产量及其构成。结果表明,在不同密度下,长沙水稻的株高和秆高,怀集早稻玉香油占的秆高及晚稻Y两优1号的株高和秆高变化不显著,而早稻Y两优1号株高和秆高变化显著,其余品种无一致的规律。在实际黄金密度下,长沙各品种有效和高效叶面积指数及其冠层光辐射截获率最高,或者低于最高密度处理,但冠层光辐射截获率与最高密度处理无显著差异;长沙和怀集各品种齐穗期和成熟期的干物质积累及其产量在实际黄金密度下最高,或者低于最高值,但产量与最高值差异不显著。长沙双季稻和怀集晚稻的矮秆品种(49.4~74.5 cm),其产量的主要贡献来源于有效穗数,而怀集早稻的高秆品种(80.4~84.6 cm),其产量的主要贡献来源于有效穗数和每穗粒数。本研究结果为合理、简便、精确确定水稻适宜的种植密度(即合理密植)提供了理论和实践依据。     

不同母质发育土壤的中红外吸收光谱特征

选取湘东丘陵区四种典型母质发育土壤(酸性紫色土、花岗岩红壤、板岩红壤和第四纪红土红壤),采集剖面(深至母岩/母质层)样品,应用傅里叶变换红外光谱仪研究灼烧去除有机质处理、土层深度和母质类型对土壤中红外吸收光谱特征的影响,分析吸收光谱与土壤理化性质的关系。结果表明,去除有机质后,特征区的中红外吸收值升高,反映矿物质对红外吸收谱线的强烈影响。在剖面上,底土(60~80 cm或100~120 cm)的中红外吸收值高于表土(0~20 cm),与土壤有机质含量的剖面分布相反。四种土壤的中红外光谱均属典型的高岭石图谱。砂粒、粘粒含量与红外吸收值的相关性最好,砂粒含量的最大相关系数(0.51)出现在3700、913和720~540 cm~(-1)附近,粘粒含量的最大相关系数(0.54)出现在1100~694 cm~(-1);本研究表明,原土的中红外吸收光谱特征主要受矿物质的支配,可以很好地反映土壤质地的状况,指示土壤质量变化。     

氮磷钾对桔梗干物质积累及桔梗皂苷D含量的影响

采用3因素3水平的盆栽正交试验研究了不同浓度N(7.5、15、30 mmol L-1)、P(0.5、2、4 mmol L-1)和K(3、6、18 mmol L-1)营养液配比对桔梗干物质积累、养分吸收利用及桔梗皂苷D含量的影响。结果表明:在N_3、P_2、K_2水平处理下桔梗叶片光和色素含量及净光合速率各自达到最大值。随着栽培时间的延长,桔梗根部干物质及N、P、K积累量逐步增加,桔梗皂苷D含量则先下降后上升,但均在10月份显著升高。N、P、K肥对桔梗干物质积累及桔梗皂苷D含量的影响顺序为氮肥钾肥磷肥。10月收获时,分别在N_2、P_2、K_2水平处理下,桔梗根部干物质积累量及桔梗皂苷D含量最大。全生育期内桔梗植株对N、P、K的吸收量为101.93、86.24、158.10 mg plant-1。且春夏季N、P、K营养在桔梗地上部分高于地下部分,而秋季营养物质向根部集中。结论:桔梗植株全生育期内对氮、钾肥需求较多,且氮肥对桔梗的生长影响最大,每生产100 kg桔梗干物质需N、P_2O_5、K_2O的比例为1∶0.90∶1.27。     

腐植酸与氮肥互作对烤烟生长和氮素吸收的影响

采用盆栽试验,研究了腐植酸的三个水平(H1:0 mg kg~(-1)、H2:300 mg kg~(-1)、H3:900 mg kg~(-1))与氮肥三个水平(N1:0mg kg~(-1)、N2:40 mg kg~(-1)、N3:120 mg kg~(-1))互作对烤烟品种中烟100生长和氮素吸收的影响。结果表明,腐植酸与氮肥互作对烤烟干物质和氮素积累的影响达到极显著水平(P0.01)。其中腐植酸用量H2、H3与氮肥N2、N3互作时,与H1N1(CK,不施肥)相比,H2N2、H2N3、H3N2、H3N3处理的烤烟干物质积累量分别提高了97.6%、89.7%、77.7%和114.4%,氮素积累量提高了1.7、1.2、1.1和2.0倍;H3(900 mg kg~(-1))与N3(120 mg kg~(-1))二者互作效果较好。     

侵蚀程度对红壤团聚体分布及养分含量的影响

[目的]探讨不同侵蚀程度下红壤团聚体和养分的变化规律,为侵蚀红壤的肥力提升和合理开发利用提供理论依据。[方法]将红壤表层按照不同深度剥离来模拟不同土壤侵蚀程度,比较分析不同侵蚀程度下团聚体稳定性、有机质和各养分的变化规律及其相互关系。[结果]各侵蚀程度红壤团聚体干筛粒级分布规律大体相似,以≥2mm粒级团聚体为优势粒级,与无明显侵蚀土壤相比,强烈侵蚀土壤≥2mm水稳性团聚体含量降低近1/3;随着土壤侵蚀程度增加,土壤碳、氮、磷等养分含量均表现出逐渐减少的规律,其中强烈侵蚀土壤有机质、全氮和全磷含量减少了30%左右,碱解氮含量减少了近50%,速效磷含量减少了80%以上。相关分析表明,土壤有机质、全氮、全磷、碱解氮含量均与≥2 mm团聚体含量、WSA,MWD和GMD值具有较好的正相关性(p0.05),与D和PAD值呈负相关。[结论]不同侵蚀程度对红壤团聚体分布及养分含量有一定影响,可通过增加有机肥来改善侵蚀红壤结构,提高土壤肥力。     

带状套作复光后不同大豆品种干物质积累模型与特征分析

为了研究套作下高产类型大豆复光后的干物质积累特征,本研究共采用14个高、中、低产量水平的大豆为材料,比较了不同大豆产量类型品种与玉米套作,复光后的干物质积累特征差异。结果表明:1)高产类型大豆复光后干物质积累量为32.99 g·plant?1,较中、低产类型分别高26.82%和91.51%(两年均值)。2)不同产量类型大豆复光后干物质积累速率均呈先增加后下降的趋势,复光后最大干物质积累速率和平均干物质积累速率呈高产类型中产类型低产类型,高产类型大豆最大干物重积累速率的时间大致在复光后41~42 d,中低产类型则在复光后33~37 d;高产类型大豆复光后干物质渐增期天数、积累速率和干物质积累量以及快增期和缓增期的积累速率和积累量均显著高于中、低产类型。3)产量与最大干物质积累速率、最大干物质积累速率时间、平均干物质积累速率、渐增期的持续时间及干物质增量、快增期平均积累速率及干物质增量、缓增期平均积累速率及干物质增量呈显著正相关。本研究表明,套作下高产类型大豆复光后较强的干物质积累优势主要表现在复光后渐增期,而复光后渐增期较强的干物质积累能力主要在于其较长的渐增期持续天数。     

基于物元评判模型的土地整理综合效益评价方法研究

利用物元分析理论,将土地整理综合效益的等级、评价指标及其特征值作为物元,确定土地整理综合效益的经典域、节域及待判物元,应用物元和可拓集合中的关联函数建立了土地整理综合效益物元评判模型。并以山西省阳高县王官屯等二乡(镇)土地开发整理项目为例,对土地整理综合效益物元评判模型进行了实证研究,其综合效益的等级属于程度Km(P)=(-0.101,0.037,-0.431),属于"一般"等级,与模糊综合评价结果相似,符合项目区的实际情况。物元模型应用于土地整理综合效益评价作为一种初步的尝试与探索,为定量评价土地整理综合效益提供了一种新的思路。     

Transitioning from standard to minimum tillage: Trade-offs between soil organic matter stabilization, nitrous oxide emissions, and N availability in irrigated cropping systems

Few studies address nutrient cycling during the transition period (e.g., 1–4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N₂O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize–tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced ¹⁵N-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 μm), microaggregates (53–250 μm) and silt-and-clay (<53 μm). We found a cropping system effect on soil N_new (i.e., N derived from ¹⁵N-fertilizer or -¹⁵N-cover crop), with 173 kg N_new ha⁻¹ in the conventional system compared to 71.6 and 69.2 kg N_new ha⁻¹ in the low-input and organic systems, respectively. In the conventional system, more N_new was found in the microaggregate and silt-and-clay fractions, whereas, the N_new of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-N_new than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-N_new was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N₂O emissions (39.5 g N₂O–N ha⁻¹ day⁻¹) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha⁻¹) produced intermediate N₂O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N₂O emissions, and N availability.     

Starving the soil of plant inputs for 50 years reduces abundance but not diversity of soil bacterial communities

If soil communities rely on plant-derived carbon, is biodiversity lost when this primary source is removed? Soil microbial and mesofaunal communities at the Rothamsted Highfield site were compared under a mixed grass sward, arable rotation and a section maintained as a bare-fallow for the past 50 years by regular tillage. Organic matter reserves have been degraded and microbial and mesofaunal numbers and mite diversity have declined in this unique bare-fallow site, where fresh carbon inputs have been drastically reduced. However, it supports a species-rich metabolically active bacterial community of similar diversity to that in soil maintained as grass sward. Thus in contrast to soil mesofauna, bacterial diversity (but not abundance) is apparently independent of plant inputs.     

青藏高原高寒草甸土壤有机质、全氮和全磷含量对不同土地利用格局的响应

草地土地利用格局的变化强烈影响着其土壤营养元素的含量与垂直分布。对青藏高原东北隅高寒草甸不同土地利用格局（封育植被、放牧利用和人工种植）下不同深度（0—10cm、10—20cm和20—40cm）的土壤有机质、全氮和全磷含量的对比研究表明：封育植被下土壤营养元素在表层和深层之间有显著差异（P〈0．05）,与土壤深度表现出一定的负线性相关（R2〉0．40,P〈0．05）。放牧利用和人工种植对营养元素在不同土壤层次的分布无显著影响（P均值〉0．05）,前者的有机质和全氮含量与土壤深度略呈负线性,后者则无此关系。放牧利用和人工种植较显著地（P均值〈0．05）降低了土壤表层有机质和全氮的含量,但增加了土壤表层全磷的含量,对土壤深层的影响较小。人工种植对营养元素含量的影响效果略大于放牧利用,但两者差异不显著。